I've come to notice, in my dealings with several different fandoms -- anime, British, sci-fi, etc. -- that there is a distinct dividing line when it comes to yaoi, or male-on-male pairings, in fanfiction, fanart, or even general discussion among friends. This is one of those fields where people either appear to love it or despise it ... I, personally, have never heard anyone say 'Well, M/M is okay, I guess,' whereas the range of feelings on yuri (female-on-female) is endless.
This could, perhaps, go back to the idea of fandom as being mostly male, a stereotype I have encountered (and been said to forcibly bend and break) many times. Of course, we must bear in mind that the 'male majority' statement has an assumed 'heterosexual' in front of it. And even there, I have known heterosexual males who own several volumes of Gundam Wing doujin and argue over accurate pairings. Add to this the fact that many of the protests one will hear over male pairings are from females, and the argument seems to fall apart. Why, then, the protests?
Let's look at fandom as a whole. When we're talking about science fiction, we're talking about Star Trek, Star Wars, and Doctor Who, with some smaller fandoms thrown in on the side. All three of these shows specialise in having sexy women in skimpy costumes. We have Shatner snogging with the good old Green Alien Girl; we have Leia and Amidala being forcibly stripped; we have Leela prancing around in next to nothing. These were made to entice the men, just as much as exploding spaceships and light saber duels.
So, in science fiction, girls take it where they can get it. Once in awhile, we get ourselves a Han Solo or a young Obi-Wan Kenobi, but much is left to our imaginations. George Lucas certainly isn't going to strip down Ewan MacGregor, no matter how much it would improve the movies. On some occasions, they'll even throw us something like Paul McGann as the Eighth Doctor, a purposely handsome and romantic character. Again, only rarely. While fandom may not be exclusive to hetero males, the makers of fandom fodder are almost nothing but. And if we make art to entertain ourselves first off ... well, who can blame them?
Where does this leave yaoi fans? Well, according to some of my reading, it gives us Lister-on-Rimmer (or vice-versa) fanfics. And while Chris Barrie is rather fetching, it isn't quite the same as all the female pairings out there. Granted, in the past two years, sci-fi/fantasy got a nice injection of handsome men with the Lord of the Rings and Harry Potter movies ... but then we're accused of slashing hairy men or old men. Anime gives us a large variety of bishonen (pretty boys) to choose from, but then they're too girly, or too butch, or something to an extreme in between. In other words, we're damned either way.
But why is this? As far as I can see, the big problem with the slash fandom stems from two main points that walk about hand-in-hand with each other:
1. Girls have different tastes. The majority of women, while still rating appearance very high subconsciously, find that they are attracted more to personalities and characters rather than to physical features. So they lust after hobbits? It's not that he's a hobbit, it's that he's Frodo. And Jason Isaacs as Malfoy? Old enough to be one's father, yes, but also 'deliciously evil.' Alan Rickman? Look no further than the voice. Feminine lust is more often than not triggered by something beyond physical appearances.
2. Girls want men the way they want them. And here, we have a problem in fanfiction and fanart more than anywhere else. If girls find an attractive man in anime, say, or in science fiction, but he doesn't fit her conception of the Perfect Man just right, she may very well change him. Take the aforementioned Malfoy. She likes his voice, his attitude, and his hair, but she doesn't like his superiority. Very well, then -- she will make him the uke (bottom -- literally, in Japanese, 'receiver'). Not only that: she will make him like it. Fanfiction, then, gets a bad rap (in other areas as well, but very prominently in slash) for taking men out-of-character and making the situations ridiculous and implausible.
But this doesn't occur as much in yuri. Why? Because girl-on-girl for most men is enough in and of itself. They don't need a plot. And for girls, the idea of romance in the face of adversity (Utena/Anthy, Yomiko/Nancy, etc. etc.) is sweet; or, for some, the idea that the girls have broken free of men who do nothing for them is liberating, and something that we can all identify with on some level.
What's the cure, then? Well-written male slash. I'm not joking. Stories such as Thank You, Jeeves (among others) manage to stay completely in-character, while still incorporating the emotional and romantic elements that many readers want. Of course, we'll never get rid of bad fic, as long as anyone can get a free website or an account on FanFiction.net, but the good writers out there deserve some recognition. As for the fans themselves -- of course it's a sin. But so is all good smut. If you don't care on your own account, don't start caring on anyone else's.